Triclinic Modification Research Articles

Synthesis and structure of antimony compounds (Ph3SbBr)2O · 2PhH and [(2-MeC6H4)3SbBr]2O · 0.5PhH

Hydrolysis of triphenylantimony dibromide or tri(o-tolyl)antimony dibromide in benzene yields the solvates (Ph3SbBr)2O · 2PhH (triclinic modification) (I) and [(2-MeC6H4)3SbBr]2O · 0.5PhH (II), in which the Sb atoms have a distorted trigonal-bipyramidal coordination. The aryl ligands are in the equatorial positions; the bridging oxygen atom and the terminal Br ligands occupy the axial positions. The bond lengths in I: Sb-C, 2.103(2)–2.125(2) A, Sb-O, 1.976(1) and 1.979(1); and Sb-Br, 2.7128(2) and 2.7592(2) A. The bond lengths in II (A): Sb-C, 2.109(6)–2.145(3) A; Sb-O, 1.954(4)–1.958(4) A; and Sb-Br, 2.7355(8)–2.7624(7) A. The angles SbOSb are equal to 138.83(6)° in I and 170.8(3)° and 161.6° in II.

Benzyl 2-(4-bromoanilino)-4,4-dimethyl-6-oxocyclohex-1-enecarbodithioate: second triclinic polymorph

The title structure, C22H22BrNOS2, is a triclinic modification. Whereas the other reported modification crystallizes with just one mol­ecule in the asymmetric unit, the present modification has Z′ = 2. The six-membered cyclo­hexene ring adopts an envelope conformation, with the C atom bearing the two methyl groups representing the flap. This atom deviates by 0.674 (4) Å from the plane passing through the other five atoms of the ring (r.m.s. deviation = 0.027 Å). For the second independent mol­ecule, the deviation is 0.669 (3) Å and the r.m.s. deviation is 0.010 Å. The mol­ecular conformation of both mol­ecules is stabilized by intra­molecular N—H⋯S hydrogen bonds.

Crystal chemistry and topology of Rb–MIII molybdates (M = Fe, Sc, In) and triclinic Rb2Mo4O13: novel building blocks, decorated chains and layers

Four different rubidium metal molybdates and Rb2Mo4O13 have been synthesised by flux growth and their crystal structures were determined from single-crystal X-ray diffraction data. The compound Rb5Fe(MoO4)4 represents a novel and unusual structure type based on isolated Fe2Mo8O22 building blocks (with a central Fe2O8 dimer composed two edge-sharing square pyramids in an up-down arrangement) linked by Rb+ cations (Cmca, a = 18.355(4), b = 10.487(2), c = 39.303(3) Å, V = 7566(4) Å3, R(F) = 3.46%, Z = 16). Rb5In(MoO4)4 is characterised by a decorated kröhnkite-like octahedral-tetrahedral chain structure (P2/c, a = 11.391(2), b = 7.983(2), c = 11.100(2) Å, β = 113.74(3)°, V = 924.0(3) Å3, R(F) = 2.27%, Z = 2). It is isotypic with Rb5Er(MoO4)4. The two compounds RbFe(MoO4)2 and RbSc(MoO4)2, both crystallise in KAl(MoO4)2-type structures in space group P-3m1, with a = 5.673(1)/5.789(1), c = 7.495(2)/7.578(2) Å, V = 208.89(8)/219.93(8) Å3, R(F) = 1.69/1.26%, respectively, Z = 1. The simple Rb molybdate Rb2Mo4O13 is triclinic and isotypic with K2Mo4O13 and the triclinic modification of (NH4)2Mo4O13. It has space group P-1, with a = 8.259(2), b = 8.402(2), c = 10.274(2) Å, α = 104.56(3) β = 106.41(3), γ = 109.90(3)°, V = 593.4(2) Å3, R(F) = 2.20%, Z = 2. The different connectivities within the structures and the role of the Rb atoms are discussed. The topologies and relative stabilities of M2Mo4O13 (M = (NH4), K, Rb, Cs, Tl) compounds and their structure types are briefly reviewed.

Beiträge zur Kristallchemie und zum thermischen Verhalten von wasserfreien Phosphaten. XXXXII Die ersten Iridiumphosphate

AbstractThe First IridiumphosphatesTwo polymorphs of iridium(III)‐metaphosphate Ir(PO3)3 and an iridium(IV)‐silicophosphate (Ir1−xSix)3[Si2O(PO4)6] (x ∼ 0.5) were synthesized and their crystal structures determined from single‐crystal x‐ray data. Pale pink needles of triclinic Ir(PO3)3 (Ru(PO3)3 structure type, $P{\bar 1}$ (No. 2), Z = 2, a = 6.9574(6) Å, b = 10.3628(9) Å, c = 5.0288(4) Å, α = 92.28(1)°, β = 92.80(1)°, γ = 98.60(1)°, 1574 independent reflections, 122 parameters, R1 = 0.028, wR2 = 0.061) were grown from a metaphosphoric acid melt. Pale pink prisms of C‐type Ir(PO3)3 (C‐Al(PO3)3 structure type, Cc (No. 14), Z = 12, a = 13.103(2) Å, b = 19.183(1) Å, c = 9.354(1) Å, β = 127.19(1)°, 4254 independent reflections, 354 parameter, R1 = 0.024, wR2 = 0.062) were obtained by chemical vapour transport (900 °C → 800 °C, addition of IrCl3·xH2O). Both metaphosphates are built of [IrIIIO6] octahedra and infinite $^{1}_{\infty}\rm (PO^{-}_{3})$ chains. The latter have a translation period of three phosphate tetrahedra in the triclinic modification and six in the monoclinic. 1D and double‐quantum filtered 2D 31P‐MAS‐NMR spectra of C‐type Ir(PO3)3 confirm the chain structure and reveal a chemical shift range between −4,8 and −30,9 ppm for the 9 crystallographically independent, however chemically similar phosphate groups.Pale orange crystals of (Ir1−xSix)3[Si2O(PO4)6] (Si3[Si2O(PO4)6] structure type, $R{\bar 3}$ (No. 148), Z = 3, a = 7.8819(8) Å, c = 24.476(4) Å, 1086 independent reflections, 56 parameters, R1 = 0.061, wR2 = 0.190) occurred in chemical vapour transport experiments aiming at the crystallization of C‐Ir(PO3)3. The crystal structure of the silicophosphate consists of isolated [IrIVO6] octahedra and [Si2O(PO4)6]12− heteropolyanions.

Crystal structure of trans-bis(trifluoro-acetylacetonato)copper(II)

Triclinic modification of trans-bis(trifluoroacetylacetonato)copper(II) is studied by single crystal X-ray diffraction (diffractometer X8 APEX BRUKER, MoKα radiation, T = 173(2) K). The structure is molecular. Square environment of the Cu atom (Cu-Oav 1.916 A, ∠O-Cu-Oav 93.4°) is completed to a bipyramid by two atoms of neighboring molecules, Cu...Cγ 3.18 A and 3.23 A.

Hydrogen bond and the structures of 2-, 3-and 4-biphenylmethanols

Density functional theory (B3LYP/6-31G*) is applied to calculate structures, energy, dipole moment, polarizability, frequencies of normal vibrations in the harmonic approximation and intensities in vibrational spectra of 2-, 3-, and 4-biphenylmethanol molecules and their H-complexes that can form in crystalline, amorphous, and liquid phases. Based on the analysis of simulation results, the effect of the position of a methanol group in the molecule on its vibrational spectrum is discussed. The structure forming role of a hydrogen bonds in biphenylmethanols and the possibility of realization of two polymorphic modifications in 2-biphenylmethanol are stated. These modifications are: metastable monoclinic, in which each of four molecules of the unit cell is a link of a chain H-associate; and stable triclinic, in which four molecules of the unit cell organize an H-complex in the form of a cyclic tetramer. It is found that crystalline samples of 3-and 4-biphenylmethanols consist of chain H-associates. A glass-like sample of 2BPhM being a mixture of H-complexes consisting of cyclic tetramers and chain associates contains crystalline nuclei of triclinic and monoclinic polymorphous modifications in the supercooled state. In a liquid sample of 2BPhm, chain H-associates and free molecules are realized.

Synthese, Struktur und EPR‐Untersuchungen von binuklearen Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(thioureato))‐Komplexen des CuII, NiII, ZnII, CdII und PdII

AbstractSynthesis, Structure and EPR Investigations of binuclear Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(thioureato)) Complexes of CuII, NiII, ZnII, CdII and PdIIThe synthesis of binuclear CuII‐, NiII‐, ZnII‐, CdII‐ and PdII‐complexes of the quadridentate ligand N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(thiourea) and the crystal structures of the CuII‐ and NiII‐complexes are reported. The CuII‐complex crystallizes in two polymorphic modifications: triclinic, $P{\bar 1}$ (Z = 1) and monoclinic, P21/c (Z = 2). The NiII‐complex was found to be isostructural with the triclinic modification of the copper complex. The also prepared PdII‐, ZnII‐ and CdII‐complexes could not be characterized by X‐ray analysis. However, EPR studies of diamagnetically diluted CuII/PdII‐ and CuII/ZnII‐powders show axially‐symmetric g and ACu tensors suggesting a nearly planar co‐ordination within the binuclear host complexes. Diamagnetically diluted CuII/CdII powder samples could not be prepared. In the EPR spectra of the pure binuclear CuII‐complex exchange‐coupled CuII‐CuII pairs were observed. According to the large CuII‐CuII distance of about 7,50Å a small fine structure parameter D = 26·10−4 cm−1 is observed; T‐dependent EPR measurements down to 5 K reveal small antiferromagnetic interactions for the CuII‐CuII dimer. Besides of the dimer in the EPR spectra the signals of a mononuclear CuII species are observed whose concentration is T‐dependent. This observation can be explained assuming an equilibrium between the binuclear CuII‐complex (CuII‐CuII pairs) and oligomeric complexes with “isolated” CuII ions.

New crystalline modification of μ-oxo-bis(bromotriphenylantimony)

The triclinic crystalline modification of μ-oxo-bis(bromotriphenylantimony) has been synthesized by the reaction of triphenylantimmony dibromide with water in benzene. The Sb atoms have distorted trigonal bipyramidal coordination with the bromine atoms and bridging oxygen atoms in the axial positions. The distances are Sb-C 2.104(2)-2.123(2), Sb(1)-Br(1) 2.7492(2), Sb(2)-Br(2) 2.7235(2), Sb(1)-O 1.986(1), and Sb(2)-O 1.987(1) A, and the Sb(1)OSb(2) angle is 138.19(6)°.

Second crystal modification of 1,10-diazonia-18-crown-6 dichloride

The second crystal modification (II) of 1,10-diazonia-18-crown-6 dichloride [H2DA18C6]2+·2Cl−, where [H2DA18C6]2+ is the 1,10-diaza-18-crown-6 dication (DA18C6) with two protonated nitrogen atoms, was investigated by XRD. The monoclinic modification (II) (space group P21/n, a = 9.600 A, b = 5.689 A, c = 15.749 A, β = 91.03°, Z = 2) was solved by direct methods and refined by full-matrix least squares analysis in an anisotropic approximation to R = 0.032 for all 2494 independent reflections collected (CAD-4 automatic diffractometer, λMoKα). In modification II, the conformation of the DA18C6 dication and the ion packing differ from those in triclinic modification I investigated previously.

Influence of polyethylene glycol template on microstructure and electrochromic properties of tungsten oxide

Electrochemical synthesis of tungsten oxide (WO 3) thin film nanostructures by potentiostatically controlling the surface aggregates formed at the electrode–electrolyte interface, in the presence of a polymeric template (polyethylene glycol 400, PEG) from a plating sol of peroxotungstic acid (PTA) is presented. The nanoparticulate morphology of the WO 3 film changes drastically upon varying PEG content in the precursor sol; from an amorphous structure with randomly distributed pores for a film derived from a PTA sol with PEG:ethanol in a 3:7 volume ratio, to a mesoporous, nanocrystalline material with hybrid structures encompassing spherical grains and nanorod-like shapes with a triclinic modification for a film formed in a sol with PEG:ethanol in a 1:1 volume ratio. This approach highlights the role of the PEG proportion in controlling crystal growth, assembly patterns and pore structure. The film derived from the sol with PEG:ethanol in a 1:1 volume ratio exhibits superior transmission modulation and coloration efficiency as compared to the film obtained from a sol with PEG:ethanol in a 3:7 volume ratio. While the latter film deteriorates rapidly within 35 color-bleach cycles, the former film sustains more than 3500 cycles, without significant degradation. This film also exhibits fast switching between the clear and blue states; these are repercussions of the mesopore structure and the interconnected nanocrystallite phase.

Isostructurality in trivalent metal tris(benzoylacetonates)

Isostructurality is a similarity of the spatial arrangement of molecules off different compounds in their crystal structures. A prerequisite for isostructurality of two compounds is isometry of their molecules. This is best achieved for molecules which differ only in one or few core atoms, while the surface of the molecule remains mostly unchanged [1]. A very good example of such systems are tris(diketonate) coordination compounds of trivalent metals. This was noticed as early as 1926 when has been noted that the crystal structures of trivalent metal pentane-2, 4-dionato complexes of various metals appear to be grouped in several isomorphous series [2]. If the metal atom is coordinated by asymmetrical diketonate, two different isomers (facial and meridial) are possible. Our work concentrated on compounds where trivalent metals are coordinated by 1-phenylbutane-1, 3-dionato ligands which were studied by single crystal X-ray diffraction and thermal analysis. The meridial complexes of iron(III), manganese(III), chromium(III) were already reported to be isomorphous based on their powder diffraction patterns [3]. We have shown that thay crystallize in the monoclinic system, space group P21/c. The only facial isomers which could be isolated where those of chromium(III) and cobalt(III) complexes. They were both found to crystallize in two pseudopolymorphic modifications. Pure compounds crystallize in the space group P– 1 with two molecules in the asymmetric unit. The crystal structures of the chromium and cobalt compounds are almost identical. Under same crystallization conditions, both compounds can also crystallize as hydrates. The hydrates crystallize in the space group R– 3 with 12 molecules per unit cell. The two symmetrically independent molecules in the structure differ in the mode of hydratation. As is the case with the triclinic modifications, the trigonal modifications of both chromium and cobalt compounds are almost perfectly isostructural. [1] A. Kalman, L. Parkanyi, G. Argay, Acta Cryst. (1993) B49, 1039. [2] W. T. Astbury, Proc. Roy. Soc. (1926) 28, 313. [3] R. C Fay, T. S. Piper, J. Am. Chem. Soc. (1962) 84, 2303.

Naphthyridines as building blocks: the helix structure of 2-N-acetylamino-7-methyl-1,8-naphthyridine

24 European Crystallographic Meeting, ECM24, Marrakech, 2007 Page s154 Acta Cryst. (2007). A63, s154 systems are tris(diketonate) coordination compounds of trivalent metals. This was noticed as early as 1926 when has been noted that the crystal structures of trivalent metal pentane-2,4-dionato complexes of various metals appear to be grouped in several isomorphous series [2]. If the metal atom is coordinated by asymmetrical diketonate, two different isomers (facial and meridial) are possible. Our work concentrated on compounds where trivalent metals are coordinated by 1-phenylbutane-1,3-dionato ligands which were studied by single crystal X-ray diffraction and thermal analysis. The meridial complexes of iron(III), manganese(III), chromium(III) were already reported to be isomorphous based on their powder diffraction patterns [3]. We have shown that thay crystallize in the monoclinic system, space group P21/c. The only facial isomers which could be isolated where those of chromium(III) and cobalt(III) complexes. They were both found to crystallize in two pseudopolymorphic modifications. Pure compounds crystallize in the space group P–1 with two molecules in the asymmetric unit. The crystal structures of the chromium and cobalt compounds are almost identical. Under same crystallization conditions, both compounds can also crystallize as hydrates. The hydrates crystallize in the space group R–3 with 12 molecules per unit cell. The two symmetrically independent molecules in the structure differ in the mode of hydratation. As is the case with the triclinic modifications, the trigonal modifications of both chromium and cobalt compounds are almost perfectly isostructural

Polymorphic transformations of C26H54 and C28H58 n-paraffins as typical rotator substances

Thermal deformations and polymorphic transformations of two long-chain evennumbered normal paraffins C26H54 and C28H58 were studied by thermal X-ray diffraction (temperature step is tenths of a degree), infrared spectroscopy (temperature step is 1–5°), and differential scanning calorimetry (temperature step is 2° in a sample heating melt cooling mode. The samples are characterized by high homologous purity (99.0%) and belong to so-called “boundary” n-paraffins. The starting C26H54n-paraffin sample is a triclinic modification at room temperature (Tccryst). When quickly cooled, the melt crystallizes as the triclinic Tccryst and monoclinic monolayer 1Mcryst forms (two-phase mixture Tccryst + 1Mcryst). The starting C28H58n-paraffin sample is a double-layer monoclinic modification 2Mcryst at room temperature. Crystallization from hexane or slow cooling of a melt leads to a monolayer monoclinic form 1Mcryst. Thermal deformations and temperature ranges of existence of the crystalline forms (Tccryst, 1Mcryst, and 2Mcryst), low-temperature rotator crystalline orthorhombic form (Orrot.1), and high-temperature rotator crystalline hexagonal (Hrot.2) phases of these n-paraffins were evaluated from changes in their diffraction patterns and unit cell parameters. The molecular structure and the conformational composition of these n-paraffins in different states were found from their IR spectra. Differential scanning calorimetry (DSC) was used to determine the phase transition temperature. Thermal X-ray diffraction, IR, and DSC data agree well with one another.

Four Distinctively Different Decomposition Pathways of Metastable Supermesityltellurium(IV) Trichloride

Chlorination of bis(supermesityl)ditelluride RTeTeR (R = 2,4,6-t-Bu3C6H2) with 3 equiv of sulfuryl chloride SO2Cl2 provided the intrinsically unstable supermesityltellurium(IV) trichloride RTeCl3 (1) as bright yellow crystals. Severe repulsion between the equatorial Cl atom and one tert-butyl group in an ortho position in the supermesityl ligand is the reason for the extreme reactivity of 1, which is in contrast to that of all previously known monoorganotellurium trihalides. In the solid state at room temperature, (the triclinic modification of) 1 reacts slowly under HCl elimination and intramolecular Te-C bond formation to give the bicyclic 5,7-di-tert-butyl-2-hydro-3,3-dimethylbenzo[b]tellurophene-1,1-dichloride (2), which was originally obtained as a colorless amorphous solid. On one occasion, when the solid-state reaction was allowed to occur under air conditions, compound 2 and a colorless crystalline byproduct, namely, trans-supermesityltellurium hydroxide dichloride (3), had formed, from which a few crystals were hand-selected. The formation of 3 has been tentatively rationalized by a solid-state hydrolysis of a second (monoclinic?) modification present in the bulk material of 1. In diethyl ether, THF, or carbon disulfide, a redox equilibrium exists between yellow supermesityltellurium(IV) trichloride RTeCl3 (1), deep blue supermesityltellurenyl(II) chloride RTeCl (4), and chlorine gas, which can be shifted to 4 when the reaction vessel is purged with argon to remove the chlorine gas. Compound 4 was also obtained by the reaction of RTeTeR (R = 2,4,6-t-Bu3C6H2) with 1 equiv of SO2Cl2. When a solution of 1 was stored with an excess of SO2Cl2 for a prolonged amount of time, Te-C bond cleavage occurred and [(Et2OH)2Te2Cl10].2Et2O (5) was formed. Compounds 1-5 have been characterized by X-ray crystallography.

Crystal structures of complexes of the cys-syn-cys isomer of dicyclohexano-18-crown-6 with oxonium hexafluorotantalate and oxonium hexafluoroniobate

The crystal structures of [(cys-syn-cys-dicyclohexano-18-crown-6 · H3O)][TaF6] and [(cys-syn-cys-dicyclohexano-18-crown-6 · H3O)][NbF6] complex compounds are determined using X-ray diffraction analysis. The tantalum complex has two polymorphic modifications, namely, the monoclinic (I) and triclinic (II) modifications. The unit cell parameters of these compounds are as follows: a = 8.507(4) A, b = 11.947(5) A, c = 27.392(12) A, β = 93.11(1)°, Z = 4, and space group P21/n for modification I; and a = 10.828(1) A, b = 11.204(1) A, c = 12.378(1) A, α = 72.12(1)°, β = 79.40(1)°, γ = 73.70(1)°, Z = 2, and space group P-1 for modification II. The triclinic niobium complex [(cys-syn-cys-dicyclohexano-18-crown-6 · H3O)][NbF6] (III) with the unit cell parameters a = 10.796(3) A, b = 11.183(3) A, c = 12.352(3) A, α = 72.364(5)°, β = 79.577(5)°, γ = 73.773(4)°, Z = 2, and space group P-1 is isostructural with tantalum complex II. The structures of all three complexes are ionic in character. The oxonium cation in complexes I–III is encapsulated by the crown ether and thus forms one ordinary and two bifurcated hydrogen bonds with the oxygen atoms of the crown ether. This macrocyclic cation is bound to the anions through the C-H...F contacts (H...F, 2.48–2.58 A). The conformation of the macrocycle in complex I differs substantially from that in complex II (III).

Ytterbium hydrogendiphosphate trihydrate: synthesis and non-merohedral twinning

The title compound, Yb(HP2O7)·3H2O, is isostructural with the other triclinic modifications of this stoichiometry.

Polymorphism of even saturated carboxylic acids from n-decanoic to n-eicosanoic acid

The polymorphism of normal saturated even carboxylic acids from n-decanoic to n-eicosanoic acid is discussed. Seven crystal modifications, including polymorphs and polytypes, were identified and fully characterized by the combination of calorimetric measurements (DSC) at atmospheric and high pressures, X-ray powder diffraction, FT-IR spectroscopy and scanning electron microscopy (SEM). All seven crystal forms, including polymorphs and polytypes, are observed at room temperature. Forms A2 and Asuper are triclinic, form C is monoclinic and forms E and B show both a monoclinic and an orthorhombic polytype. The triclinic modifications A2 and Asuper predominate for acids up to n-tetradecanoic acid (C14H27O2H). The orthorhombic and the monoclinic forms predominate for acids from n-hexadecanoic (C16H31O2H) up to n-eicosanoic acid (C20H39O2H). When the temperature is increased, all the crystal modifications transform irreversibly to the C form. In the first part of this paper, cell parameters for the different forms are given, the observed temperatures and enthalpies of the transitions are reported and the stability of the different forms is discussed. In the second part, we state the main contribution of each technique for the identification and interpretation of the polymorphism of even numbered carboxylic acids.

Study of retinoic acid polymorphism

Some authors recently hypothesized the existence of a new retinoic acid (RA) phase in addition to the two already known polymorphs. We investigated RA polymorphism and our results exclude the presence of new modifications and refine the properties of the known forms. By comparison of simulated and acquired X‐Ray Powder Diffraction (XRPD) it was possible to identify only the known monoclinic (I) and the triclinic (II) modifications; the same were also characterized by DSC, IR, and Raman spectroscopy. A solubility study associated to DSC allowed establishing an enantiotropic relationship between the two forms, with form II being less stable (ΔGII/I = 0.71 kJ/mol at 37°C) below the transition temperature (136.6°C; ΔH = 3.2 kJ/mol). The intrinsic dissolution rate (IDR) (I = 61 µg/cm2 × min−1; II = 125 µg/cm2 × min−1) confirmed this energetic relationship. The kinetics of solid transition I → II was examined and its activation energy estimated (356 kJ/mol). The attempts to produce new phases allowed the development of methods to obtain the two polymorphs with high chemical and polymorphic purity. A validated DSC method is presented that enables detection of the presence of form I at a level of 1% (w/w) when in mixture with form II.

A comparison of electrochromic properties of sol–gel derived amorphous and nanocrystalline tungsten oxide films

A pristine acetylated peroxotungstate sol with and without 4 wt% of oxalic acid dihydrate (OAD) yielded nanocrystalline and amorphous tungsten oxide (WO3) films respectively by dip coating technique. Contrary to the expected trend, whereby, the nanostructured 4% OAD film with a triclinic modification should have shown superior electrochromic efficiency, its amorphous 0% OAD counterpart exhibits higher optical modulation and coloration efficiency at photopic wavelengths. This anomalous behavior of the amorphous 0% OAD film was correlated to a higher W5+ content in its colored state. The colored nanocrystalline 4% OAD film contained a lower proportion of the W5+ color centers. Under the same level of lithiation, while the 4% OAD film was also constituted by W4+ states, its 0% OAD counterpart did not contain any 4+ states of tungsten. X-ray photoelectron spectroscopic (XPS) investigations also confirmed that the single peak at ∼1.4 eV in the absorption coefficient–wavelength spectrum of the colored 0% OAD film arises from the small polaronic transitions between the W6+ and W5+ states of tungsten whereas the W6+–W5+ and the W5+–W4+ charge transitions produce two distinct peaks at 1.2 and 1.6 eV in the α–λ spectrum of the colored 4% OAD film. The microstructure of the 4% OAD film, characterized by an interconnected network of nanocrystallites and pores promotes rapid ion insertion and extraction. Therefore, the larger magnitudes of NIR reflectance modulation, diffusion coefficient for lithium, electrochemical activity and faster color–bleach kinetics observed for the 4% OAD film, are a direct consequence of its structure. Band gap widening upon lithium insertion observed for both films, is a repercussion of Burstein–Moss effect and structural changes that occur upon coloration.

An orthorhombic modification of (R)-(−)-8-hydroxy-3-methyl-3,4-dihydro-1H-2-benzopyran-1-one [(R)-(−)-mellein

In addition to the known triclinic modification of the title compound, an ortho­rhom­bic modification is now described. In the crystal packing of the title compound, C10H10O3, the mol­ecules are linked via inter­molecular C–H⋯O hydrogen bonds into infinite chains which extend in the [100] direction and are stacked along [001].